Electric switching device



P 22, 1953 v. G. KRENKE 2,653,198

ELECTRIC SWITCHING DEVICE Filed Jan. 22, 1952 2 Sheets-Sheet 1 Fig.2.

Fig.20. Fig.2l.

2 I I w 24 ,22

@fi. I LJ LJ WITNESSES: INVENTOR Vincent G.Krenke.

ATTORNEY Patented Sept. 22, 1953 UNITED STATES ENT FFI CE ELECTRIC SWITCHING DEVICE Application January 22, 1952, Sofia-1N0. 267,545

Claims. 1

This invention relates generally to electric switching devices and more particularly to such devices which are generally classified as electrical interlocks.

Such devices usually comprise a push rod or plunger-operated switching mechanism used for various switching operations in circuits. In the application of these interlocks to electrical circuits, the circuit requirements may be such as to indicate normally open interlock switching in some instances, normally closed interlock switching in other instances and in still other instances both. As a general rule in the assembly of electric control panels wherein such switching is required, electrical interlocks of the two different types, namely the normally closed contact type and the normally open contact type, must be stocke'di.

In view of this situation, in an eiiort to minimize the stocking of varieties of different items, attention has been devoted in the past to the development of electrical interlocks which could be assembled or modified on the job to provide either of the two types of switching mentioned. Such operations, however, are time consuming and for the most part are not entirely satisfac- 'tory.

Accordingly, it is a principal object of this invention to provide an electrical interlock of the character generally referred to, which is operable either as a normally open or normally closed switching device.

Further to the preceding object, it is an object of this invention to provide such an electrical interlock which may be used; either as a normally open or normally closed interlock without the need of disassembling or reassembiing the mechanism.

More specifically stated, it is an object of this invention to provide an electrical interlock of the character generally described having two mounting faces and suitable mechanism wherein by mounting the interlock on one mounting face, normally open interlock operation may be obtained, and by mounting the interlock on the remaining mounting face, normally closed interlock operation maybe obtained.

A general object of this invention is to provide an interlock of the character hereinabove referred to which is simple with respect to operational remiirements, positive in operation, and easily manufactured.

foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will be- .2 come apparent upon a study of the following disclosure when considered in conjunction with the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of an electrical interlock embodying the principles of this invention;

Figs. 2 through 6 are details of several of the components of the interlock of Fig. 1;

Fig. '7 is a modification of the invention illustrated in Fig. 1.;

Figs. '8 and 9 illustrate details of certain of the structural components of Fig. 7;

Fig. 10 is a side elevational view of another embodiment of this invention;

Fig. 11 and 12 are respectively end and top views in elevation of the structure of .Fig. 10;

Fig. 13 illustrates the interlock of Fig. 10 arranged for normally closed contact operation;

Figs. 14 through 18 illustrate certain structural details of the embodiment of this invention shown in Figs. 10 through 13;

Fig. 19 is a variation of the structure illustrated "in Fig 15 and Figs. 20, 21 and 22 show a further variation of the structure of Fig. 1 5.

In general, this electrical interlock accomplishes the aforesaid objects in the manner in which the interlock plunger is mounted in the interlock casing. In all of the arrangements illustrated herein, the plunger is slidably mounted by suitable guide means which in turn is slidably mounted in the interlock casing. The guide means is movable between two positions, and in this operation carries the plunger and movable contact mounted on the plunger between the mentioned two positions. In one'position of the guide means, the movable contact is completely disengaged from the stationary contacts of the interlock. In the other position of the guide means, the movable contact is engaged with the stationary contacts, affording by means of this simple manipulation of the guide means selective normally closed or normally open operation of the interlock.

One specific structure functioning according to the aforesaid general principle, is illustrated in Fig. 1 and comprises generally a casing l which is arranged in two halves la and lb. Stationary contacts 2a and 2b ar secured between the two sections of the casing la and It at the time of assembly. Openings 3a and 3b are provided in the respective casing sections to and it in positions in opposite ends of the assembled casing structure and slidably receive therein for limited outward movement the respective guide members 4a. and 4b. These guide members, as illustrated, are identical and as better seen in Figs. 4 and. 5, are provided with outwardly projecting flanges 5, which engage suitably shaped surfaces of the respective openings Sc and 3b to limit the outward travel of the guide members. These guide members may be extrusions of sheet material or may be molded articles of any suitable material. Moreover, any suitable means for limiting the indicated outward movement of the respective guide members may be utilized.

A plunger 6 is slidably mounted through the openings id and lb of the respective guide members. This plunger is a stamping of sheet material provided with a spring-receiving slot 8 having spring guide projections 9a and 9b projecting inwardly of the slot 8 from each end thereof. A coil spring It under a predetermined degree of compression is fitted over the spring-receiving projections 59a and 9b, and seats in the extremities of the slots 8. The length of this slot and consequently the position of the respective ends of the compression spring Ill correspond to a pr determined normal spacing of the guide members s ta and db along the plunger 6 for the specific interlock casing which has been illustrated.

The respective end faces lo and id of the casing ections constitute the mounting faces of the interlock assembly. The details in which the interlock may be secured on a mounting surface, such as H, which is only fragmentarily shown, have not been illustrated in the interest of simplicity since any of the numerous conventional mounting means may be utilized.

When the interlock is mounted with the face id against a suitable mounting surface or panel, such as H, having an opening l2 therein sufliciently large to clear the bottom end of the plunger 6, as viewed, the guide member ib is moved inwardly of the interlock casing to a position in which its outer face is flush with the surface id of the bottom section of the interlock casing. The inner edge of the opening lb in the guide member 4b abuts the bottom end of compression spring it and moves the plunger E to the position illustrated. The upper guide member ta rides the upper end of the compression spring it, and as a consequence is thrust outwardly of the interlock casing to a position in which the locks 5 engage the corresponding surfaces of the opening 3a in which position the movement is stopped. As earlier noted, this position corresponds substantially to the position occupied by the upper end of the slot 8 in the plunger 6.

The movable contact assembly is also a stamping of sheet material which for this application is preferably a good conductor of electric current since the movable contact conducts current between the respective stationary contacts 2c and 2b. The plan view of the movable contact is illustrated in Fig. 2, and a sectional view taken on the line IIIIII of Fig. 2, and differing from that illustrated in Fig. 1, appears in Fig. 3. This movable contact i3 is provided with a slot i l of sufiicient width to clear the coils of the spring it. Projections !5 project inwardly from each end of the slot [4 in the movable contact. This movable contact is resiliently attached to the plunger by a pair of springs [6 which are disposed between respective mounting or spring plates ll fitted over respective projections E8 on the plunger and the respective projections on the movable contact.

The arrangement is such that the springs are in compression when the movable contact is in the position illustrated against the stationary contacts 2a and 2b or when the movable contact rides against the stops is and 5 which are integrally formed with the upper interlock casing section la. The normal position of the contacts when this assembly is mounted upon the surface id for the closed position which is as illustrated.

If under these conditions a force is applied to the upper end of the plunger 6 to effect movement thereof downwardly against the force of the spring 8, the spring it is compressed, and the projections it on the plunger move downwardly through the plane of the movable contact to a position below this plane in which the force of the springs It has a component directed towards the stops Be and if. This force drives the movable contact in a snapeacting movement from its position contactingthe stationary contacts into engagement with the stops ie and i to open the electrical connection across the stationary contacts. When the force is removed from the plunger ii, spring bias returns the plunger to the position illustrated in which the spring-carrying projections it on the plunger 8 again cross the plane of the movable contact, and with a snapacting movement, the movable contact is engaged with the two stationary contacts.

If it is desired to operate the interlock of Fig. l as a normally open switching device, the entire assembly is inverted, and the end face ic or" the interlock casing is positioned on the mounting surface i i with the end of the plunger 6 projecting through the opening l2 in the mounting surface in the same manner as illustrated. In this instance, the guide member 40 is moved inwardly of the interlock casing until its outer face is flush with the plane of the mounting face lc. The entire plunger assembly is moved by the force applied thereto through engagement of guide member 5a with the end of the compression spring It. Projections it of the plunger pass through th plane of the movable contact 9 ii, and the toggle action of springs it moves the movable contact into a position engaging the stops is and If. The other end of the compression spring it, which engages guide member ib, new thrusts this guide member outwardly of the interlock casing to a position corresponding to that illustrated in connection with guide member ta, and the switch is now ready for use as a normally open switching device.

Although the snap-acting toggle-type operation of the movable contact, which has bea. illustrated in Fig. 1, may be desirable for certain circuit applications, such switching action is not required in every application. In Fig. 7, a type of mounting of a movable contact 20 is provided in which make and break operation at a speed corresponding to the speed of movement or" a plunger 2! is obtained. In Fig. 7, parts corresponding to those of Fig. l bear like reference characters.

Plunger l in this application is of the con figuration illustrated in Fig. 9 and is provided with two slots 2:2 and 23, each having springreceiving projections 2d projecting inwardly from the ends of the slots. The inner ends of these slots are symmetrically disposed with respect to the geometric center lengthwise of the plunger and are spaced apart a distance corresponding to the thickness of the movable contact 2%.

Movable contact 26 is provided with a slot 25 slightly larger dimension in length and in width than the cross-sectional dimensions of plunger 21. This movable contact is slipped over the plunger :2l, and thereafter the springs 26a and 25b are positioned in the respective slots '22 and 23 over the projections :24 to resiliently secure the movable contactsubstantially centrally of the plunger.

As in the case .of .Fig. 1, this movable plunger is mounted in suitable guide members do and 4b which are slida'bly fitted in the respective openings 3a and 3Tb in the respective casing sections to and ll) of the interlock casing I. The .stationary contacts 2a and :2b are again clamped between the respective casing sections Id and ID in positions to intercept the movable contact in its movement with the plunger. The interlock is assembled on the surface it in normally open position. In this arrangement, the guide member Ab projects inwardly of the interlock casing and the guide member do projects outwardly of the casing.

In its inoperative position, the plunger is supported in the position shown, that is, it is prevented from axial movement through the respective guide members :by the spring .2611 and 2617.

as viewed, until such time as movable contact 29 disengages the stationary contacts. Spring 26b then restores the plunger 2% to its normal position.

As in the case of Fig. 1, this interlock assembly maybe operated as a normally closed switching device by the simple expedient of inverting the assembly on the surface H, which reverses the positions of the respective guide members .411 and ib with respect to the interlock housing and moves the plunger therewith to a position in which the movable contact 2&3 engages the stationary contacts. When so mounted, application or force to the opposite end of plunger 2| separates the movable contact 29 from the stationary contacts. in this operation, compression spring 2 5a alone supplies the biasing force.

In the embodiments of the invention hereina'bove considered, no consideration has been made with regard to structural symmetry, for example,

of the sections la and lb of the interlock casing.

It is believed that structural symmetry of such items is desirable from a manufacturing point of view since the number of production tools required to produce the parts for the unit may thereby be minimized. Inasmuch as such design problems are believed to be within the capacities Figs. 10, 11 and 12, illustrating an improved embodiment of this invention.

By particular reference to Fig; 10, itwill be seen that the interlock casing 2'! is comprised of a pair of identical upper and lower sections as viewed, designated 21d and 2%. The general structural features of this interlock arrangement 6 are in principle to those illustrated in Figs. 1 and 57, and :aliord certain advantages .thereover, :as will :beapparent from the following discussion.

In this assembly, a pair of identical stationary contacts are gripped between the respective housing sections 2111 and .271). These stationary contents are designated '28:: and 28b, and are provided with similarly shaped offset contact ends. These ends project into the casing into positions to :be straddled by the movable contact 29.

The plunger 3d of this embodiment is detailed in planform in Fig. 14 and is provided with a pair of spaced slots ilfla and 30b adjacent opposite ends thereof, and is further provided with .T-shaped projections due and 36d which project laterally thereof at the center of the plunger. These projections provide spring seats 30c which are spaced apart a distance correspondin to the thickness of the movable contact 23. The mova'ble contact is provided with a longitudinal slot of .a :width corresponding to the thickness of the plunger material and of the length to straddle the T-shaped projections 39c and 30d.

The plunger is slidably mounted in a yoke 3| which is comprised of two identical stamped and formed sheet metal sections 31d and Slb of the general configuration illustrated in perspective in Fig. 15. Opposite ends of this yoke are provided with U-shaped section Slc which are displaced in the same direction from the plane of the section and of an internal width correspondi-ng to the thickness of the plunger 30. The depth of the u -shaped section tic corresponds roughly to a little more than half the width of the plunger body. When these items are assembled as illustrated in Fig. 10, for example, the U-shaped sections 3l-c forming a bearing or guide for slidin-g movement of the plunger therethrough. The distance between the outer ends of the respective slots 33a and 35b in the plunger corresponds to the internal longitudinal dimension of the respective yoke sections.

In the assembly of this structure, the movable contact 29 is slipped over the plunger it to its normal position centrally thereof. Respective spring plates 32 are then slipped over the "plunger from opposite ends thereof to abut opposite sides of the movable contact 29. Respective springs 33a and 331) are then slipped over the opposite ends of the plunger 3%, the inner ends of these springs abutting the respective spring plates 32. The outer ends of of the springs 33a and 332; are shaped as illustrated in the perspective detail of Fig. 16, having a diametrically disposed end piece 330 fitting through the respective slots 30a and 30b in positions engaging the confronting inner ends of the yokes assembled about the plunger. Thus, outward travel of the outer ends of the respective springs is limited by the respective slots 39a and 33b, while travel of the mentioned outer ends of the springs inwardly or in compression is obtainable within the limits ,.of the lengths of the respective slots Silo and 39b.

The respective ends 210 and Zid of housing sections 21a and 2117 are provided with openings of the configuration shown in Fig. 18. In this figure, a circular opening 3 is provided with diametrically disposed slots 3%. The diameter of the opening 3 1 is sufli-cient to clear the dimension across the U-shaped sections of the assem'bled yoke, and the dimension between the bottoms of the slots 34a is sufficient to clear the side sections of the .assembled yoke and function as a guide for the side sections to prevent rotation of the yoke in the interlock casing.

The longitudinal dimension of the yoke is greater than the dimension across the faces 21c and 21d of the interlock casing. As a consequence, when the interlock is mounted on any one 'of its mounting surfaces, for example, the surface 21:55 as shown in Fig. 10, the bottom end of the yoke is moved upwardly into the plane of the mounting surface, and the upper end projects above the top of the casing. In view of the connection between the yoke and the plunger by means of the respective springs 330; and 331), the plunger assembly including the movable contact is displaced upwardly with respect to the casing to a position in which the movable contact is disengaged from the stationary contacts. This constitutes the normally open position of the interlock assembly. When force is applied to the upper end of the plunger 3:: moving the plunger downwardly, spring 33a is compressed at the time movable contact 29 engages the stationary contacts. Spring 33a is moved in compression until the downward limit of travel of the plunger is reached. When the plunger is released, both springs thrust the plunger upwardly, and when movable contact 25 disengages the stationary contacts, spring 33?) returns the plunger to the position illustrated.

In this construction, provision is made to limit the extent of axial movement of the plunger and yoke assembly with respect to the casing to that which is required for positioning either end of the yoke in the plane of the respective mounting faces 27c and Zld. This is accomplished by means of lugs 3ld which project from opposite sides of the yoke in diagonally disposed positions. These projections or lugs, when the yoke is assembled, occupy positions longitudinally of the yoke assembly, and consequently constitute a limit of movement for either direction of movement of the plunger and yoke assembly with respec to the casing. By making the sections of the yoke with the diagonally disposed projections 31d, the sections of the yoke may be assembled in face-toface relation without regard for the positions of the projections as would be the case if but one lug per section were used.

Alternatively, the yoke 3| may be a molded item, as illustrated in Fig. 19, and designated 3 if.

Such a'molded item may be a semi-cylindrical structure having a slot dig longitudinally disposed centrally thereof for the purpose of clearing the movable contact 29 and further provided with the slots 3 [h in the respective ends to receive and guide sliding movement of the plunger 3%. Projections or lugs 31k correspond to projections Sid of Fig. 15. The principles of this construction, together with its function, will be understood from the discussions concerning the respective yoke sections 3m and 31b.

Figs. 20, 21 and 22 are three views of a single piece plunger guide having box-shaped end sections it interconnected by legs ll which are spaced apart laterally a distance sufiicient to clear contact supporting springs such as 33a and 33b. The end faces of sections Ml are each rectangularly slotted at 62 to receive the plunger such as 39. Lugs '54 project from the slotted end faces to prevent the plunger guide from sliding out of the housing after assembly. The same principles regarding overall plunger guide length apply here as in the structure of Fig. 10, for example.

Fig. 13 illustrates the application of the embodiment of the invention in Fig. 10 as a normally closed interlock. In accomplishing this, as in the previously described embodiments, the interlock assembly is inverted, the surface 210 being mounted upon the indicated mounting surface. The yoke and plunger assembly is now displaced in a direction to engage the movable contact 29 with the stationary contacts 28a and 28b. Some overtravel is provided in this case as in the previously described cases so that the contact faces are engaged before the end of the yoke is positioned in the plane of the mounting face 210. Thus, the spring 33a is compressed, and a contact making force is applied to the contact assembly.

Ihe arrangement shown in Fig. 13 can be modified to operate a little differently by eliminating the upper por ion of the housing, as viewed, securing the plunger guide in the bottom part of the housing, providing a slightly stiffer spring 33a than 331) so that contact 29 when released from contacts 28a and 2% will occupy a normally open position thereabove and riveting contacts 28a and 28bin the position shown so that they may be swung aside about the rivet to release moving contact 29 which would then be forced up by spring 33b to a position above contacts 28a and 2th for normally open operation, after which contacts 280; and 28?; are swung back.

From the foregoing considerations, it will be appreciated that the various objects of this invention hereinbefore enumerated, together with other objects which have since become obvious, have been accomplished in each of the several embodiments herein illustrated and described, and that these objects are accomplished by the simple expedient of affording a degree of relative movement between a plunger and a plunger guide, and slidably mounting such plunger guide in the interlock casing.

In the illustration and description of this invention, certain specific structures for accomplishing the given end have been illustrated. l-Iowever, there are many other ways in which this basic mechanical principle may be practiced in such structures without departing from the spirit and scope of this invention. For example, in all of the illustrated embodiments, the guide means has been designed to project from the casing so that when a particular mode of operation of the interlock is desired, it may be easily obtained by the simple expedient of mounting the roper surface of the interlock casing against the mounting handle or surface for the interlock. The guide means by engagement with the surface of the mounting panel is therefore moved in the proper direction and in the proper amount to pre-position the interlock mechanism for the required mode of operation.

While it is thought that such an arrangement represents a convenient and substantially foolproof design, it will be appreciated that this same principle may be practiced with guide or yoke assemblies which do not project from the interlock casing but which lie wholly within the interlock casing. Such guide means may then be reached through suitable access holes in the casing proper with a screwdriver or other suitable instrument, and pushed in the required direction to lock the movable contact assembly in a posi tion to give the required mode of operation. With such an arrangement, the guide means may be suitably frictionally engaged with the casing so that movement during normal operation will not obtain, or stated otherwise. so that move- 9 mm unlessby the instrume tality su gested wi not occur.

Likewise, although this. interlock has. b en. 11 1. trated with a singlev set. of contacts which are bridged by the longitudinal d m nsion o a current. carrying movable contact, will be apprecie ated that. contact assemblies involving bridging of stationary contacts across, its lateral dimension at each end of the, movable contact, mayalso be provided.

Accordin ly. it i in nded ha h foregoin disclosure and the showings made in the drawing shall be considered only as illustrative of the principles of this invention and not interpreted in a limiting sense.

I; claim s my nv ntion 1.

1. An ele trical switch interlockcomnrisine, a. casing having ope in s. throu h ppos te n faces thereof, guide means slidably supported in said openings, 3, plunger slidably mounted in said guide means and projecting out of said guide means at each end of said casing, spring means axially disposed of and mounted on said plunger, said spring means having displaceable end portions on said plunger adjacent confronting portions of said guide means, stationary contact means mounted in said casing, movable contact means mounted on said plunger to move therewith between positions engaging and disengaging said stationary contact means, the outer end o faces of said guide means defining a dimension therebetween greater than the dimension between said end faces of said casing, said guide means being movable between two positions in said casing and moving said plunger therewith, affording selectively normally open and normally closed positioning of said movable contact with respect to said stationary contact means.

2. An electrical switch comprising, a casing having openings through opposite end faces iv thereof, contact actuating means including a plunger and guide means slidably engaging said plunger at spaced points on said plunger, said guide means being slidably mounted in said openings, spring means on said plunger having end portions displaceably engaged with said plunger at said spaced points, corresponding portions of said guide means engaging said end portions of said spring means, the outer end faces of said guide means defining a dimension greater than the dimension across the end faces of said casing, stationary contact means mounted in said casing, movable contact means mounted on said plunger for movement with said plunger between positions engaging and disengaging said stationary contact means, said guide means because of engagement with said spring means being effective to displace said plunger and movable contact between normally open and normally closed contact positions upon sliding movement of said guide means through said openings.

3. An electrical switch comprising, a casing having openings through opposite end faces thereof, stationary contact means mounted in said casing, a plunger, spring means axially disposed of said plunger and having end portions displaceably connected to said plunger at spaced points therealong, guide means slidably mounted in said openings and slidably mounting said plunger through said casing, corresponding confronting end portions of said guide means engaging said end portions of said spring means, said guide means having a dimension across the outer end faces thereof greater than the dimension across the opposite end faces of said casing, movable. contact. means mounted on a d pl n e to more th ew th between posi ns e ga i and ngagin sai st tionary contact mea s, aid guide means bee us of:- eneaeeme t. w h d prin means bein efieoti e o di p a e said plun erand. movable ontact betwe n n ma ly pen n rm lly losed; onta positi s p n sliding movement, oi uide rou h.

. :onen ns ele triea swit h ompris n a cosinev having openin s pposite. nds; the f, statienaru e nt ct means mo nte in said ca in a planner. spr m an axially dispo d of said p unger nd hav n end portion d p y ted: sa d plun erat axia y spac d movabie contact means mount d on aid age? snide means slidably mounted in said ough engagingsaid end portions ofsaid spring means, sl ing movement of said a. d m ans. thr u h said openin s d p a ing sa d lunger and movable contact means with respect to said stationary contact, means between normally open and normally closed contact posionsel etrical switch compris ng, a no. stationary contact means mounted in said casing, guid means ida ly mounted in said. casing, a plunger slidably mounted in said guide means, movable contact means mounted on said plunger, spring means on said plunger and engageable with said guide means for biasing said guide means and said plunger toward given relative axial positions, said guide means being movable between two positions in said casing and moving said plunger therewith, afiording selectively normally closed and normally open positioning of said movable contact with respect to said stationary contact means.

6. An electrical switch comprising, a support, stationary contact means mounted on said support, guide means slidably mounted on said support, a plunger slidably mounted on said guide means, movable contact means slidably mounted on said plunger, spring means interconnecting said plunger, said guide means and said movable contact means for biasing said plunger, said guide means and said movable contact means into a given relative axial relationship; said guide means being slidable on said support between two positions, respectively, normally engaging and normally disengaging said moving contact means with said stationary contact means.

7. An electrical switch comprising, a support, stationary contact means mounted on said support, guide means slidably mounted on said support, a plunger slidably mounted on said guide means, movable contact means slidably mounted on said plunger, spring means interconnecting said plunger, said guide means and said movable contact means for biasing said plunger, said guide means and said movable contact means into a given relative axial relationship; said guide means being slidable on said support between two positions, respectively, normally engaging and normally disengaging said moving contact means with said stationary contact means, and projections at spaced points on said guide means engageable with cooperating portions of said sup port for limiting the extent of sliding movement of said guide means on said support.

8. An electrical switch comprising, a support, stationary contact means mounted on said support, a moving contact, a plunger slidably mounting said moving contact, guide means comprising a and lidablyniountine said plun er a pair of sections having slots therein, said guide means straddling said plunger from opposite sides thereof and slidably mounting said plunger in said slots, spring means engaging said guide means, said plunger and said moving contact for biasing said guide means, said plunger and said moving contact into a given relative axial relation, said guide means being slidable on said support between two positions respectively normally engaging and normally disengaging said moving contact with said stationary contact means.

9. An electrical switch comprising, a support, stationary contact means mounted on said support, a moving contact, a plunger slidably mounting said moving contact, guide means comprising a pair of sections having slots therein straddling said plunger from opposite sides thereof slidably mounting said plunger in said slots, spring means engaging said guide means, said plunger and said moving contact for biasing said guide means, said plunger and said moving contact into a given relative axial relation, said guide means being slidable on said support between two positions respectively normally engaging and normally disengaging said moving contact with said stationary contact means, and projections at longitudinally spaced points on at least one of said sections and engageable with cooperating portions of said support for limiting the extent of sliding movement of said guide means on said support.

10. An electrical switch comprising, a support, stationary contact means mounted on said support, a plunger guide slidably mounted on said support and having a pair of interconnected longitudinally spaced end sections each having an opening therein,-a plunger slidably fitted through the openings in said plunger guide, a pair of compression springs coaxially disposed about said plunger, the outer ends of said compression springs each releasably engaging a cooperating portion of said plunger adjacent the respective end sections of the plunger guide, a moving contact slidably disposed on said plunger between said compression springs, said plunger guide being slidable on said support between positions normally engaging and disengaging said moving contact with said stationary contact.

VINCENT G. KRENKE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,925,585 Friedman Sept. 5, 1933 2,106,581 Unwin Jan. 25, 1938 2,424,527 Whyte et a1 July 22, 1947 

